Standard Emf Research Articles

Corrosion Resistance Analysis of Al-Cu, Al-Zn and Al-Cu-Zn Alloys

Anticipating an alloy's corrosion resistance is essential to avoid product failure and reduce costs. Research and analyze the corrosion resistance of Al-Cu, Al-Zn and Al-Cu-Zn alloys based on the analytical balance of the elements according to weight, thermodynamic, metallurgical rules on metal alloys, kinetic and other properties. The purpose of this study is to determine the corrosion resistance of Al-5-wt% Cu, Al-5-wt% Zn and Al-5-wt% Cu-5-wt% Zn alloys based on the analytical calculation. Based on the analytical calculation results, the Al-Zn-Cu alloy has the best corrosion resistance with a corrosion rate of 0.4375 mmpy. Next is the Al-Cu alloy with a corrosion rate of 0.4634 mmpy. While Al-Zn alloy has the lowest strength with a corrosion rate of 0.4828 mmpy. Based on standard EMF potential values for these three alloys. Al-Zn alloys are most active with an value of-1.61 V, followed by Al-Zn-Cu alloys with an value of - 1.60 V, and the noblest Al-Cu alloy has the most positive value of-1.56 V. Faraday's law to get corrosion rates of the anode and cathode materials. In the third reaction, the exothermic alloy has a positive value of so the exothermic reaction occurs.

Electrochemical Separation of Barium into Liquid Bismuth by Controlling Deposition Potentials

Electrochemical separation of barium from multi-component molten salt electrolyte (BaCl2-LiCl-CaCl2-NaCl) at 500–700°C is demonstrated using a liquid bismuth electrode which possesses strong chemical interactions with barium. While the standard emf analysis suggests Na to be the first species to deposit in this electrolyte followed by Ca, Li, and finally Ba, barium was found to be the first species to be reduced into the bismuth electrode followed by Ca. The exceptional deposition behavior of barium was ascribed to the activity of the constituent alkali/alkaline-earth metals in the bismuth metal. The activity of barium in bismuth was extremely low (as low as 10−15), shifting the redox potential of barium to the most positive potentials and enabling the separation of barium into liquid bismuth. By exploiting the differential interactions of constituent ions with the liquid bismuth, it was possible to separate conventionally non-separable barium species from the electrolyte solution. In addition, high coulombic efficiencies of the liquid bismuth electrode (>99%) suggest that electrode processes are chemically reversible for co-deposition of barium and calcium. The analyses of electrode potentials at various current densities and electrochemical impedance spectra indicate charge transfer as the most significant overpotential mechanism during electrolysis.

Potentiometric Cells with Liquid Junctions: A Combined Analytical and Computational Study

It is known that the electromotive force (emf) of cells with transference is dependent on an integral involving electrical transport numbers, t i , and chemical potentials. However, the origin of this integral, the conditions under which it is valid, its properties and utility are not well understood. This article aims to clarify such aspects. A general emf equation is derived in a manner in which the integral arises from the entropy production due to diffusion. Five important properties of the equation are recognized: (1) invariance with respect to the reference frame for t i measurements, (2) redundancy of single-ion activities, (3) lack of a potential function for the integral when the number of independent t i is greater than 1, (4) irrelevance of any metric on the junction 3-D space, and (5) invariance with respect to the free-diffusion time. As an application, the emf equation is tested for calibration of cells with dissimilar electrodes and junctions between the saturated potassium chloride solution and hydrogen chloride solutions in a range of concentration. It is found that (1) the standard emf can be estimated with a precision of about 0.1 mV for accurate enough data sets, and (2) the free-diffusion model is more appropriate for the flowing junctions than the continuous mixture model, although the difference between the two models is slight. In similar systems with less concentrated potassium chloride solutions, the free-diffusion mass density profiles are found to bear a sign of convective instability, because of which previously reported steady emfs for such cells may pertain to a changed solution composition in one of the two half-cells.

Thermodynamics of Cadmium Chloride in 2-Butanone + Water Mixtures (5, 10, and 15 Mass%) from Electromotive Force Measurements

The emf (electromotive force) of the cell: CdHgx (two phase) | CdCl2 (m) | AgCl | Ag in 2-butanone + water mixtures (containing 5, 10, and 15 mass% 2-butanone) was measured at varying temperature (293.15, 298.15, 303.15, 308.15, and 313.15 K) and in the CdCl2 molality range from 0.002 to 0.02 mol-kg−1. At each temperature the standard emf of the cell (Emo) was determined using potentiometric data and literature values for the stability constants of chlorocadmium complexes. The Emo values were used to calculate the standard thermodynamic quantities for the cell reaction, the stoichiometric mean molal activity coefficients of CdCl2, and the thermodynamic functions for CdCl2 transfer from water to 2-butanone + water mixtures. The transfer process is a forced one and results in an entropy decrease. The transfer functions were compared to those obtained for the same electrolyte in acetone + water mixtures, as well as to those for HBr in ketone + water mixtures. Medium effects upon CdCl2 were calculated and discussed for the examined mixtures (2-butanone + water).

Indirect standard electromotive force data for the H2∣HCl∣AgCl∣Ag cell for methanol–water solvents with low water content

A procedure is described whereby electromotive force (emf ) data from a cell with solid state electrodes, conventionally used for the quantitative detection of residual water in methanol–water solvents, can be used to enhance existing standard emf data in the lower water range for the cell Pt(s), H2(g)|HCl (solution in MeOH–H2O)|AgCl(s)|Ag(s)|Pt(s).

Autoprotolysis Constants and Standardization of pH Measurements in Tetrahydrofuran-Water Mixtures

Standard emf for the cell Pt/Ag/AgCl/HCl in THF-water/GE (glass electrode) in tetrahydrofuran-water mixtures containing 0–70% (w/w) of tetrahydrofuran and values of the autoprotolysis constants, Kap, of these media were obtained. The influence of variations in the solvent composition on pKap values was evaluated. The resulting equations enables us to determine pKap values in any tetrahydrofuran-water mixture, and thus permit one to establish the pH scale in these mixtures. The quasilattice quasichemical (QLQC) theory of preferential solvation was applied to obtain the degree of preferential solvation of hydrogen ions in these media, in order to explain the variation of the pKap values obtained in the tetrahydrofuran-water mixtures studied.

Thermodynamics of NaCl in Aqueous Ethylene Glycol, Acetonitrile, and 1,4-Dioxane Mixtures from Emf Measurements at 25°C

The electromotive force of the amalgam cell {NaxHg1-x‖NaCl(m)‖AgCl‖Ag} has been measured at 25°C as a function of the mole fraction x of Na in amalgams and of the molality m of NaCl in (ethylene glycol + water), (acetonitrile + water), and (1,4-dioxane + water) mixed solvents, containing up to 0.8 mass fraction of the organic component, with relative permittivities e ≥ 27. The relevant standard molal electromotive forces \(E_{\text{m}}^ \circ \) have been determined, together with the mean molal activity coefficient γ± of NaCl as a function of its molality. In the case of (ethylene glycol + water) mixtures, a linear dependence of \(E_{\text{m}}^ \circ \) on the mass fraction of ethylene glycol is observed, which is quite unusual, The Debye-Huckel equation is applicable successfully over the whole range of molalities explored, which extends to the vicinity of the solubility limit of NaCl in each solvent. The dependence of the standard emf on the logarithm of the volume fraction of water in the aqueous-organic solvent mixtures have been analyzed in terms of Feakins and French's theory, leading to a primary hydration number 7.2 for NaCl, in good agreement with previous results employing different methods.

The use of glass sodium electrodes for thermodynamic studies of sodium iodide solutions in methanol + n-propanol, methanol + iso-propanol and n-propanol + n-butanol mixtures at 298.15 K

The electromotive forces of the cells glass electrode(Na)|NaI|AgI, Ag in methanol + n-propanol (MeOH + n-PrOH), methanol + iso-propanol (MeOH + i-PrOH) and n-propanol + n-butanol (n-PrOH + n-BuOH) were measured at 298.15 K. The values of standard emf of the cells and the Gibbs energies of transfer of NaI Δ G t 0 were determined taking into consideration ion-pair formation. The enthalpies of transfer of the electrolyte were calculated using the standard enthalpies of solution of NaI obtained earlier. The values of the entropies of transfer were also obtained. The usefulness of glass sodium electrodes for thermodynamic studies of electrolyte solutions in a system containing two-component organic mixtures was evaluated and discussed.

Thermodynamic Studies of Copper(II) Sulfate in Aqueous Mannitol from Electromotive Force Measurements

Abstract Electromotive force measurements of the cell Cu–Hg/CuSO4(m)/Hg2SO4(s)/Hg have been made at 288, 298, 308, and 318 K for mannitol composition X=5, 15, and 25% (w/w) in water. The standard emf values of the cell at different temperatures and at different composition of mannitol + water mixtures have been determined by an extrapolation method. These have been utilized to evaluate the mean activity coefficient of copper(II) sulfate. The standard free energy for the cell reaction, and the primary medium effects upon CuSO4 have been evaluated. The standard thermodynamic quantities for the process of transfer of CuSO4 from water to the mannitol solution have been calculated from the values of the standard potential. The transfer parameters have been split into the electrostatic and chemical contributions and the results have been explained in the light of ion–solvent interactions and structural contributions to solvents.

The use of glass ion-selective electrodes for thermodynamic studies on electrolyte solutions 1:1 in water-organic solvent systems: Studies in the water-THF system

The EMF of the cell glass electrode (Na)¦NaCl¦AgCl,Ag in water-tetrahydrofuran (THF) mixtures containing 0, 2.5, 7.5, 10, 15, 20, 25, 30 mol% THF has been measured within the temperature range 293.15–308.15 K. Standard EMF and thermodynamic functions of transfer of NaCl (Δ GXXX t, - TΔ S tXXX,Δ H tXXX) from water to water-THF mixtures were also determined. The values obtained have been compared with the corresponding values obtained by other authors. The possibilities of using cation-selective glass electrodes for thermodynamic studies on electrolyte solutions in systems containing aprotic solvents-water mixtures are evaluated including a critical review of the opinions of other authors.

Thermodynamic studies of NaCl solutions in water + methanol mixtures by means of a galvanic cell containing a glass sodium electrode

The emf of the following cell: glass electrode (Na){NaCl}Ag/AgCl was measured in water + methanol mixtures containing 0, 5, 10, 20, 40 and 60 wt% of methanol at seven temperatures. The values of the standard emf and the thermodynamic functions of NaCl transfer (δ G t °, − TΔ S t ° and Δ H t °) were determined. The values were then compared with the corresponding ones obtained by other authors.

Thermodynamics of the hydrogen-silver chloride cell in ethanol-water mixtures from ?10 to +40�C

From emf E measurements of the reversible cell $$Pt|H_2 (g,1 atm)|HCl(m)|AgCl|Pt$$ at 0.01<m<0.1 mol-kg−1 in 70% (w/w) ethanol-water solvent mixtures over the temperature range from −10 to +40°C, the standard emf E° of the cell with the related thermodynamic functions of the cell reaction and the mean molal activity coefficients of hydrochloric acid have been determined. The present E data at 70% (w/w) ethanol have been combined with earlier data at ≤50% (w/w) ethanol to be analyzed critically by a one-stage multilinear regression method leading to an optimized set of E° values for the range 0–70% (w/w) ethanol which are essential for the assessment of pH standards in these solvent media.

The apparent molar heat capacity of aqueous hydrochloric acid from 10 to 140�C

The apparent molar heat capacity of aqueous HCl, Cp,ϕ, has been measured at temperatures of 25, 76, 103, 125 and 140°C and molalities from 0.1 to 1.02 mol-kg−1 using a Picker flow microcalorimeter. The results were analyzed using the Pitzer and the Helgeson-Kirkham-Flowers models to derive standard state heat capacities. The fitted parameters were also used to extrapolate the standard EMF of the silver-silver chloride reference electrode at steam saturation from 0 to 200°C and the mean ionic activity coefficient, γ± (HCl,aq) to 225°C, with an accuracy at the highest temperature of 2 mV and 4%, respectively. The results confirm that experimental values of Cp,ϕ to just over 100°C can be used to extrapolate standard state and excess Gibbs energies above 250°C, when the corresponding enthalpies at 25°C are accurately known.

Standard electromotive force of the H 2-AgCl;Ag cell in 30, 40, and 50 mass% glycerol/water from −20 to 25 °C: p K2 and pH values for a standard “Mops” buffer in 50 mass% glycerol/water

Data are presented regarding the establishment of the pH (designated pH ∗) of a standard buffer solution suitable as a pH reference in 50 mass% glycerol/water mixtures at temperatures ranging from −20 to 25 °C. The buffer material selected was the ampholyte Mops [(3- N-morpholino)-propane sulfonic acid], and the reference standard consists of equal molal amounts of Mops and its sodium salt. The assignment of pH ∗ values is based on measurements of the electromotive force (emf) of cells without liquid junction of the type: Pt;H 2(g,1 atm) ¦ Mops, Na Mopsate, NaCl ¦ AgCl;Ag and the pH ∗ was derived from a determination of K 2, the equilibrium constant for the dissociation process (Mops) ±/ah (Mopsate) − + H +. The standard emf of the silver-silver chloride electrode in 30, 40, and 50 mass% glycerol/water mixtures was determined from emf measurements of the cell at subzero temperatures with HCl solutions replacing the buffer-chloride mixtures.

Standard electromotive force of the H 2AgCl;Ag cell in 30, 40, and 50 mass% dimethyl sulfoxide/water from −20 to 25 °C: p K2 and pH values for a standard “Bicine” buffer solution at subzero temperatures

The establishment of the pH (designated pH∗) of a standard buffer solution suitable as a pH reference in 30, 40, and 50 mass% dimethyl sulfoxide ( DMSO) H 2O mixtures at temperatures in the range −20 to 0 °C is reported. The buffer material selected was the ampholyte Bicine ( N,N-bis(2-hydroxyethyl)glycine), and the reference standard consists of equal molal quantities of Bicine and its sodium salt. The assignment of pH∗ values rests on measurements of the emf of cells without liquid junction, Pt;H 2(g, 1 atm) ¦Bicine, Na Bicinate, NaCl ¦AgCl;Ag, and the pH∗ was derived from a determination of K 2, the equilibrium constant for the dissociation process (Bicine) ± ⇄ (Bicinate) − + H +. The standard emf in the DMSO H 2O solvents at subzero temperatures was determined from emf measurements of the cell with solutions of HCl replacing the buffer-chloride mixture.

Application of multilinear regression analysis to the evaluation of the standard EMF of the hydrogen—silver/silver chloride cell in methanol + water mixtures over wide ranges of temperature and composition

The one-stage multilinear regression method previously applied to the analysis of emf data for aqueous electrochemical cells as a function of temperature and solute concentration has been extended to the analysis of emf data for the cell: Pt|H 2|HCl ( m), CH 3OH( x), H 2O (1 − x) | AgCl|Ag as a function of methanol mole fraction ( x) as well as solute molality ( m) and temperature. In this way discrepancies between various sets of data are revealed and the consistent set of data for the standard potential of the cell so obtained can be used for the evaluation of thermodynamic acid dissociation constants and standard reference pH values in this important, much studied mixed aqueous solvent system.

Thermodynamic studies of sodium bromide in 2-propanol—water mixtures (10, 30 and 50 wt.%) from electromotive force measurements

The emf of the cell: Pt|Na(Hg)|NaBr(m), w wt.% 2-propanol—water mixture|AgBr, Ag has been measured with w = 10, 30 and 50 at temperatures of 293.15, 303.15 and 313.15 K in the molality range of NaBr from 0.04 to 0.18 mol kg−1. From these data the standard emf of the cell has been obtained and by utilizing data from the literature for the E0 of Ag/AgBr electrode the standard potential of sodium amalgam electrode has been determined. Mean activity coefficients of NaBr and thermodynamic functions ΔG0t, ΔH0t and ΔS0t for transfer of NaBr from water to 2-propanol—water mixtures have also been calculated. Thermodynamic quantities of transfer have been compared to those for the HBr electrolyte.

Thermodynamic behaviour of hydrochloric acid in propylene glycol and its aqueous mixtures from electromotive force measurements

The standard potentials of the silver-silver chloride electrode in pure propylene glycol (PG) and in nineteen PG+water solvent mixtures, covering the whole range of solvent composition, were determined from electromotive force measurements of cells of the type: Pt, H2 (gas, 1 atm): HCl (m) in solvent: AgCl, Ag, at twelve different temperatures from 0 to 55°C at 5°C intervals. The molality, m, of HCl ranged from 0.001 to 0.1 mole kg−1. The standard EMF was determined by an extrapolation method making use of the extended terms of the Debye-Hückel theory. The temperature variation of the standard EMF was used to calculate the standard thermodynamic functions for the cell reaction and the standard thermodynamic quantities for the transfer of HCl from water to the respective solvents. The results are discussed both in terms of the acid-base behaviour of the solvents and also their structural effects on the transfer process.

Theoretical background of brine electrolysis: the standard emf of the cell Pt|Cl 2|NaCl|Na(Hg) at elevated temperatures

On the basis of recent determinations of standard electrode potentials of chlorine electrode and of the concentration cell NaNa(Hg), and taking into account the temperature dependence of molal heats of individual reaction components, the values of reversible voltage of NaCl electrolysis in an amalgam electrolyser under standard as well as non-standard reaction conditions were calculated for the temperature region 25–100°C. Simultaneously, standard electrode potentials of sodium and sodium—amalgam in aqueous solutions in the temperature range 25–97.83°C (up to the melting point of sodium) were also calculated.

Determination of absolute transfer free energies of hydroxyl ion from water to aqueous 2-methoxy ethanol

Absolute standard free energies of transfer ΔGt0 of OH− from water to aqueous mixtures of 2-methoxy ethanol (ME) have been evaluated at 298.15 K by combining the apparent transfer free energies of the lyate ion that were obtained from the standard emf's of the double cell:[Formula: see text]and that from the autoionization constants of these mixed solvents determined by use of the cell comprising H2– and Ag–AgCl electrodes. The required ΔGt0 values of K+ and H+ were determined earlier using the well-known tetraphenyl arsonium tetraphenyl boride (TATB) reference electrolyte method. These values and their non-Born type contributions in particular, are found to be increasingly positive in water-rich compositions, indicating that the relative stabilization of OH− and the acidity of the mixed solvents decrease with increasing cosolvent composition. These, when compared with those in aqueous mixtures of ethylene glycol and 1,2-dimethoxy ethane, are found to lie intermediate between the latter solvent systems conforming to what is expected from the structural and electronic features of the cosolvents.